Graded Si 1-x Ge x waveguides with tight mode confinement in a broadband range of mid-infrared wavelengths are presented. Optimum TM mode confinement is observed due to the vertical variation of the refractive index. These waveguides show good potential for implementation as passive elements in mid-infrared optical circuits where strong mode confinement is required for a broadband range of wavelengths. Keywords—mid-infrared; Si 1-x Ge x waveguides; mode confinement; broad band single mode polarization To date, Silicon photonics has proved to be an enabling platform that provides integrated low-cost solutions for several applications including biosensing, imaging, computing, all-optical signal processing or high speed data communications, among others [1]. However, and despite the large variety of works reported so far by worldwide research institutions, most of them only focus on a narrow window of operation wavelengths that spans from the visible range up to the near infrared, typically up to 1.55 µm. Thus, little exploration has been done in the mid-infrared range. Only lately, and especially since the commercialization of Quantum Cascade lasers, renewed interest has been triggered on integrated mid-infrared photonics. Interestingly, many molecules have their fundamental vibrational modes in that wavelength range, which provides a promising scenario for the development of highly sensitive label-free mid-infrared sensors. In that line, a complete new set of light sources is also foreseen in this wavelength range by exploiting the non-linear properties in silicon-related materials. As a matter of fact, silicon has demonstrated to be a good material choice to accomplish such purpose, since it has a suitable nonlinear refractive index and is transparent up to 8 µm. Consequently, silicon waveguides showing supercontinuum generation or optical parametric oscillation have been already demonstrated [2,3]. Similarly, Ge and Si 1-x Ge x alloys have also been suggested as primary raw materials in mid-infrared photonic building blocks due to the extended transparency window up to 12 µm and the highest third order susceptibility compared to silicon (at 5 µm χ 3